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Weather 101 - Cloud Formations
You wouldn’t leave the dock without first checking the local weather forecast. You can get weather information from TV, radio, your VHF radio and on the Internet (see Safety Links above). While on the water, your VHF radio is the best source for weather warnings. Even so, at certain times of the year weather can change rapidly and you should continually keep a "weather eye" out, especially to the west, in order to foresee changes which might be impending.
Clouds are a tool you can use to predict or forecast weather. The type of cloud and direction of movement can warn you of weather changes that are imminent. Clouds are categorized by the altitude at which they appear and the shape that they take.
(This is not an in-depth study of clouds, but an attempt to simplify the subject for use by recreational boaters.)
It is helpful to remember the following definitions of cloud shapes:
Variations of cloud types are created by combining the cloud’s shape/description with the altitudinal names as a prefix or suffix.
Cirros (high) or Cirro can be used with cumulus (heap) to indicate a cirrocumulus or high, lumpy cloud. Cirrocumulus clouds, sometime called "mackerel skies", can indicate the approach of a hurricane in the tropics. It can also be used with stratus (flat, layered)as in cirrostratus to indicate a high, flat or layered cloud.
Alto can also be used with cumulus and stratus to indicate altocumulus and altostratus which are middle altitude lumpy clouds and middle altitude layered clouds respectively.
Nimbo or nimbus might be used with cumulus or stratus to indicate a cloud formation that is producing precipitation. These clouds could be either cumulonimbus which would be a lumpy, vertically-rising rain cloud or nimbostratus which would be a sheet or flat-looking rain cloud.
High clouds exist above 18,000 feet and are cirrus clouds.
Medium high clouds occupy altitudes of 6,500 feet to 18,000 feet. These clouds are called alto clouds. Alto clouds are used to predict weather changes in 6 to 12 hours.
Low clouds, called stratus clouds, are at altitudes up to 6,500 feet. These clouds form a solid sheet or layer of cloud mass.
Clouds with vertical growth
If you still can’t remember all of the cloud names and formations, you can always watch the clouds for two specific weather situations that indicate a high probability of a storm:
Other things to look for that indicate an approaching weather change:
IF A STORM IS NEAR…